This invention relates to a method and apparatus for the penetration of an abnormal human tissue or other objectionable biological growth, protrusion or obstruction on the surface of or within the human body for surgical purposes and with reduced thermal damage to adjacent normal tissue. More particularly, the invention relates to the removal through the use of a special laser of an abnormal biological growth or obstruction under conditions which reduce thermal and/or acoustic damage to adjacent normal tissue. A special feature of the invention also relates to the concentration of the laser beam and the resulting reduction in the treatment area.
In recent years, lasers have become of importance in microsurgery because of their ability to produce relatively bloodless incisions of great precision. In some instances, laser beams typically Nd-YAG or CO.sub.2 with respective wavelengths of 1.06 .mu.m and 10.6 .mu.m, have been transmitted through optical wave guides to an abnormal tissue growth or obstruction and used to penetrate and sever the objectionable material from remaining tissue. Typical findings with these lasers have been that significant tissue damage has occurred with the magnitude of injury being proportional to total delivered laser energy. These findings have also indicated that calcified as well as noncalcified plaques were penetrated with similar levels of injury.
One of the major problems with conventional lasers used in this treatment is that the high energies used to remove tissue often cause significant thermal and/or acoustic damage to surrounding tissue. Particularly in the removal of an construction from within a blood vessel, thermal damage may weaken an adjacent wall of the vessel or result in penetration of the wall. Therefore, a new technique for removing human tissue would be desirable.
Accordingly, one object of this invention is the removal of human tissue with a low degree of thermal and/or acoustic damage. Another object is the removal of human tissue with a more effective use of laser energy for the desired incision. These and other objects will become apparent from the following detailed description.